Torque limiter and power transmission device

ABSTRACT

A torque limiter, fixed to a flywheel including an annular portion to which knock pins each including a trunk portion are fixed, is disclosed. The torque limiter includes a first plate, a second plate axially opposed to the first plate, a friction disc disposed between the first and second plates, a pressing member, and a third plate. The pressing member presses the second plate onto the friction disc. The third plate holds the pressing member together with the second plate therebetween. The third plate includes knock pin through holes such that the knock pin are fitted therein. The third plate is attached at an attachment surface thereof to the flywheel. A length between a surface of the pressing member, facing an interior of an accommodation portion of the flywheel, and the attachment surface of the third plate is shorter than a length of the trunk portion of each knock pin.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No. 2019-181990, filed on Oct. 2, 2019. The contents of that application are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a torque limiter, particularly to a torque limiter that is accommodated in a flywheel including an accommodation portion and is positioned together with the flywheel by knock pins. Besides, the present invention relates to a power transmission device including the torque limiter.

BACKGROUND ART

A type of hybrid vehicle including an engine and an electric motor, for instance, uses such a torque fluctuation absorbing device having a torque limiter function as described in Japan Laid-open Patent Application Publication No. 2008-89017 in order to prevent transmission of an excessive torque from an output side to an engine side in engine start and so forth.

The torque fluctuation absorbing device described in Japan Laid-open Patent Application Publication No. 2008-89017 is provided with a damper part, including a pair of plates and a plurality of torsion springs, and a torque limiter disposed on an outer peripheral side of the damper part. The damper part and the torque limiter are accommodated in an accommodation portion provided in a flywheel. The flywheel is provided with an annular portion on the outer peripheral side of the accommodation portion. A plate of the torque limiter is fixed to the annular portion by a plurality of bolts.

The torque fluctuation absorbing device described in Japan Laid-open Patent Application Publication No. 2008-89017 is accommodated in the accommodation portion of the flywheel. Because of this, when the torque limiter is enlarged to reliably have a required torque capacity, this inevitably results in increase in radial dimension of the entirety of a device including the flywheel. In view of this, it can be assumed to form at least one opening in a member composing an outer peripheral part of the torque limiter in order to avoid interference between this member and an internal member of the torque limiter, and simultaneously, achieve compactness in size of the torque limiter.

However, when the torque limiter is provided with the at least one opening, the internal member is exposed through the at least one opening. Therefore, it is concerned that the internal member exposed therethrough interferes with part of the flywheel. Specifically, in assembling the torque limiter to the accommodation portion of the flywheel, there are high chances of causing interference between such a constituent member of the torque limiter as described above and part of the flywheel, because the torque limiter and the flywheel are not radially positioned at this point of time.

BRIEF SUMMARY

It is an object of the present invention to enable a torque limiter accommodated in an accommodation portion of a flywheel to reliably have a required torque capacity, and simultaneously, inhibit interference between the torque limiter and part of the flywheel in assembling the torque limiter to the flywheel.

(1) A torque limiter according to the present invention is fixed to a flywheel including an annular portion and an accommodation portion and is disposed in an interior of the accommodation portion except for a part thereof fixed to the flywheel. The annular portion of the flywheel is a portion to which a plurality of knock pins, each including a trunk portion, are fixed. On the other hand, the accommodation portion of the flywheel is provided on an inner peripheral side of the annular portion.

The present torque limiter includes a first plate, a second plate, a friction disc, a pressing member and a third plate. The first plate is a member to which a torque is inputted from the flywheel. The second plate is disposed in axial opposition to the first plate. The friction disc is disposed between the first plate and the second plate. The pressing member presses the second plate onto the friction disc. The third plate interposes and holds the pressing member together with the second plate therebetween. The third plate is provided with a plurality of knock pin through holes in an outer peripheral part thereof such that the plurality of knock pins are fitted therein at the trunk portions thereof. The outer peripheral part is attached at an attachment surface thereof to the annular portion of the flywheel.

Besides, a length between a surface of the pressing member, facing the interior of the accommodation portion, and the attachment surface of the third plate is set to be shorter than a length of the trunk portion of the each of the plurality of knock pins.

In the present torque limiter, the pressing member causes the first plate and the second plate to interpose and hold the friction disc therebetween. The torque, outputted from the flywheel, is transmitted to the friction disc through the first plate and is then transmitted therefrom to an output side. When the torque inputted to the friction disc from the flywheel is excessive in magnitude, the friction disc slips while being interposed and held between the first plate and the second plate. Accordingly, the excessive torque is prevented from being transmitted to the output side.

Here, the length between the surface of the pressing member, facing the interior of the accommodation portion, and the attachment surface of the third plate is set to be shorter than the length of the trunk portion of each knock pin. Because of this, the trunk portions of the plurality of knock pins of the flywheel start being inserted into the plurality of knock pin through holes of the third plate (corresponding to a surface at which the torque limiter is attached to the flywheel) before the pressing member is accommodated in the accommodation portion. Therefore, when the torque limiter is assembled to the accommodation portion of the flywheel, the flywheel and the third plate (i.e., the torque limiter) are radially positioned before the pressing member is accommodated in the accommodation portion.

Because of this, even when the third plate is provided with at least one opening to prevent the flywheel from interfering in part with the third plate and the pressing member is exposed through the at least one opening, interference between the pressing member and the flywheel can be avoided.

(2) Preferably, the annular portion of the flywheel includes a plurality of attachment portions disposed in circumferential alignment. Each of the plurality of attachment portions includes a protruding portion protruding radially inward. In this case, the third plate preferably includes a support portion, a tubular portion and a fixation portion. The support portion supports the pressing member. The tubular portion is provided in an outer peripheral part of the support portion. The tubular portion covers an outer peripheral surface of the friction disc. The tubular portion is shaped to axially extend in opposition to an inner peripheral surface of the annular portion of the flywheel. The fixation portion is provided with the plurality of knock pin through holes and is fixed to the flywheel. Besides, in this case, the tubular portion includes a plurality of openings disposed in circumferential alignment. Each of the plurality of openings is disposed in a corresponding position to the protruding portion so as to avoid interference between the third plate and the protruding portion.

The annular portion of the flywheel is herein provided with the plurality of attachment portions such as bolt fastening portions. Besides, each attachment portion includes the protruding portion protruding radially inward in order to maintain enough strength by reliably having a required thickness, and simultaneously, achieve compactness in size of a device including the flywheel.

In the configuration described above, the tubular portion of the third plate covers the outer peripheral surface of the friction disc. In other words, the torque limiter includes the tubular portion in the outermost diameter region of a part thereof accommodated in the accommodation portion of the flywheel. Besides, the tubular portion is provided with the plurality of openings. Furthermore, the plurality of openings are disposed in corresponding positions to the protruding portions of the flywheel. Hence, interference between the flywheel and the third plate can be avoided. Because of this, the torque limiter is enabled to reliably have a required torque capacity, and simultaneously, increase in radial dimension of the entirety of the device including the flywheel can be inhibited.

(3) Preferably, an outer peripheral surface of the tubular portion of the third plate has a diameter greater than a minimum inner diameter of the protruding portion.

Here, the tubular portion of the third plate has a relatively large outer diameter. Hence, the friction disc, disposed on the inner peripheral side of the tubular portion, can be increased in diameter. Consequently, this enables increase in torque capacity of the torque limiter.

(4) Preferably, the pressing member is a cone spring disposed in an interior of the tubular portion of the third plate.

(5) Preferably, the first plate is fixed together with the fixation portion of the third plate to the flywheel.

(6) Preferably, the first plate and the second plate are non-rotatable relative to each other.

(7) A torque limiter embedded damper device according to the present invention includes the torque limiter configured as any of the above and a damper unit. The damper unit is provided on an output side of the torque limiter and attenuates fluctuations in rotation transmitted thereto.

(8) A power transmission device according to the present invention includes a flywheel and the torque limiter. The flywheel includes an annular portion, to which a plurality of knock pins each including a trunk portion are fixed, and an accommodation portion provided on an inner peripheral side of the annular portion. The torque limiter is configured as any of the above and transmits the torque inputted thereto from the flywheel to an output-side member.

Overall, according to the present invention described above, a torque limiter, accommodated in an accommodation portion of a flywheel, is enabled to reliably have a required torque capacity, and simultaneously, interference between the torque limiter and part of the flywheel can be inhibited in assembling the torque limiter to the flywheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a power transmission device according to a preferred embodiment of the present invention.

FIG. 2 is a front view of the power transmission device shown in FIG. 1 except for a flywheel.

FIG. 3 is a front view of the flywheel.

FIG. 4 is a diagram showing a positional relation between a knock pin and a through hole with which the knock pin is engaged.

FIG. 5 is a partial enlarged view of FIG. 1.

FIG. 6 is a partial enlarged view of FIG. 1.

FIG. 7 is a partial front view of a damper ring.

DETAILED DESCRIPTION [Entire Configuration]

FIG. 1 is a cross-sectional view of a power transmission device 1 according to a preferred embodiment of the present invention. The power transmission device 1 includes a flywheel 2 and a torque limiter embedded damper device 3. On the other hand, FIG. 2 is a front view of the power transmission device 1 except for the flywheel 2. In FIG. 1, an engine is disposed on the left side of the power transmission device 1, whereas a drive unit, including an electric motor, a transmission and so forth, is disposed on the right side of the power transmission device 1.

[Flywheel 2]

The flywheel 2 is fixed to an engine-side member (not shown in the drawings). As shown in FIGS. 1 to 3, the flywheel 2 is a disc-shaped member and includes an annular portion 4 and an accommodation portion 5. It should be noted that FIG. 3 is a front view of the flywheel 2.

The annular portion 4 is provided in the outermost peripheral part of the flywheel 2. As shown in FIGS. 2 and 3, a plurality of screw holes 4 a are provided on the drive unit-side (right side in FIG. 1) surface of the annular portion 4, and besides, a plurality of knock pins 6 are fixed to the drive unit-side surface of the annular portion 4. The plural screw holes 4 a, each having a predetermined depth, are disposed at predetermined intervals in the circumferential direction. On the other hand, the plural knock pins 6 are provided at predetermined intervals in the circumferential direction. As shown in FIG. 4, each knock pin 6 includes a trunk portion 6 a and a taper portion 6 b. The trunk portion 6 a is made in the shape of a column and has height H (the length of the trunk portion 6 a protruding from the surface of the annular portion 4 of the flywheel 2). The taper portion 6 b extends from the distal end of the trunk portion 6 a and is shaped to gradually reduce in outer diameter therefrom.

Surrounding regions of the screw holes 4 a of the annular portion 4 are provided as bolt fastening portions 4 b (exemplary attachment portions). Each bolt fastening portion 4 b includes a protruding portion 4 d protruding radially inward from an inner peripheral surface 4 c of the annular portion 4. Because of this, the surrounding region of each screw hole 4 a has a predetermined thickness. In other words, each bolt fastening portion 4 b has enough strength.

The annular portion 4 is provided with a plurality of recesses 4 e. The recesses 4 e are provided to be recessed radially outward from the inner peripheral surface 4 c of the annular portion 4 in regions not provided with the bolt fastening portions 4 b.

The accommodation portion 5 is provided radially inside the annular portion 4. The accommodation portion 5 has a predetermined depth from an attachment surface of the annular portion 4 to the engine side. Besides, as shown in FIG. 3, the accommodation portion 5 is provided with a plurality of through holes 5 a in the inner peripheral part thereof in order to fix the flywheel 2 to the engine-side member.

[Torque Limiter Embedded Damper Device 3]

The torque limiter embedded damper device 3 (hereinafter simply referred to as “damper device 3” on an as-needed basis) is a device fixed to the annular portion 4 of the flywheel 2 in order to limit a torque transmitted between the engine and the drive unit, and simultaneously, attenuate rotational fluctuations. The damper device 3 includes a torque limiter unit 10 and a damper unit 20.

[Torque Limiter Unit 10]

The torque limiter unit 10 limits a torque transmitted between the flywheel 2 and the damper unit 20. As shown close-up in FIGS. 5 and 6, the torque limiter unit 10 includes a damper cover 11 (exemplary first plate), a pressure ring 12 (exemplary second plate), a friction disc 13, a cone spring 14 (exemplary pressing member) and a damper ring 15 (exemplary third plate).

The damper cover 11 is an annular plate and includes a friction portion 11 a, a fixation portion 11 b and a plurality of engaging through holes 11 c.

The friction portion 11 a is provided in the inner peripheral part of the damper cover 11, whereas the fixation portion 11 b is provided on the outer periphery of the friction portion 11 a. The fixation portion 11 b is provided with a plurality of fixation through holes 11 d and a plurality of knock pin through holes 11 e (see FIG. 4). Bolts are fastened into the screw holes 4 a of the flywheel 2 respectively, while penetrating through the fixation through holes 11 d respectively. The damper cover 11 is thereby fixed to the surface of the annular portion 4 of the flywheel 2. On the other hand, the knock pin through holes 11 e are provided in corresponding positions to the knock pins 6 of the flywheel 2.

The plural engaging through holes 11 c, axially penetrating the damper cover 11, are provided radially between the friction portion 11 a and the fixation portion 11 b. The plural engaging through holes 11 c, each elongated in the circumferential direction, are disposed at predetermined intervals in the circumferential direction.

The pressure ring 12 is an annular plate disposed in axial opposition to the friction portion 11 a of the damper cover 11 at a predetermined interval. The pressure ring 12 includes a plurality of pawls 12 a.

The plural pawls 12 a are disposed on the outer peripheral end of the pressure ring 12 at equal angular intervals in the circumferential direction. The pawls 12 a are provided to extend axially toward the damper cover 11 from the outer peripheral end of the pressure ring 12 and are engaged with the engaging through holes 11 c of the damper cover 11, respectively. Therefore, the damper cover 11 and the pressure ring 12 are non-rotatable relative to each other.

The friction disc 13 is disposed between the friction portion 11 a of the damper cover 11 and the pressure ring 12. The friction disc 13 includes a core plate 16 and a pair of friction members 17 fixed to the both lateral surfaces of the core plate 16 by rivets. Here, one of the friction members 17 makes contact with the friction portion 11 a of the damper cover 11, whereas the other makes contact with the pressure ring 12.

The cone spring 14 is disposed between the pressure ring 12 and the damper ring 15. The cone spring 14 presses the friction disc 13 through the pressure ring 12 onto the friction portion 11 a of the damper cover 11.

The damper ring 15 is disposed closer to the engine than the pressure ring 12. The damper ring 15 supports the cone spring 14 together with the pressure ring 12 therebetween, while the cone spring 14 is set in a compressed state. As shown in FIG. 5, the damper ring 15 includes a support portion 15 a, a tubular portion 15 b and a fixation portion 15 c.

The support portion 15 a has an annular shape and is provided in the inner peripheral part of the damper ring 15. The support portion 15 a is axially opposed to the pressure ring 12 and interposes and holds the cone spring 14 together with the pressure ring 12 therebetween

The tubular portion 15 b is shaped to extend axially toward the damper cover 11 from the outer periphery of the support portion 15 a. The tubular portion 15 b is disposed to cover the outer peripheral surface of the friction disc 13, while a predetermined gap is produced therebetween. As shown in FIG. 7, the tubular portion 15 b includes a plurality of first openings 15 d and a plurality of second openings 15 e. The first openings 15 d are disposed at predetermined angular intervals in the circumferential direction. This layout is true of the second openings 15 e as well.

As shown in FIG. 3, the first openings 15 d are provided in corresponding positions to the bolt fastening portions 4 b of the flywheel 2. Here, as described above, the protruding portion 4 d of each bolt fastening portion 4 b is shaped to protrude radially inward from the inner peripheral surface 4 c of the annular portion 4 of the flywheel 2. Besides, the diameter of the outer peripheral surface of the tubular portion 15 b is greater than the minimum inner diameter of the protruding portion 4 d of each bolt fastening portion 4 b of the flywheel 2. Because of this, in order to avoid interference between the tubular portion 15 b and the protruding portion 4 d of each bolt fastening portion 4 b, each first opening 15 d is shaped to avoid making contact with the protruding portion 4 d of each bolt fastening portion 4 b in the corresponding position to the protruding portion 4 d.

As described above, the plural second openings 15 e are provided at predetermined angular intervals in the circumferential direction. The pawls 12 a of the pressure ring 12 pass through the second openings 15 e, respectively. Therefore, even when the radial position of each pawl 12 a of the pressure ring 12 and that of the tubular portion 15 b of the damper ring 15 are identical to each other, each pawl 12 a and the tubular portion 15 b can be avoided from interfering with each other.

The fixation portion 15 c extends radially outward from the distal end of the tubular portion 15 b. As shown in FIG. 7, the fixation portion 15 c is provided with a plurality of fixation through holes 15 f and a plurality of knock pin through holes 15 g. The fixation through holes 15 f are provided on the outer peripheral side of the first openings 15 d, respectively. The damper ring 15 is fixed together with the damper cover 11 to the annular portion 4 of the flywheel 2 by bolts that pass through the fixation through holes 15 f, respectively. In more detail, the damper ring 15 is attached to the annular portion 4 of the flywheel 2, whereas the damper cover 11 is attached while interposing the damper ring 15 together with the flywheel 2 therebetween. Besides, the knock pin through holes 15 g are provided in corresponding positions to the knock pins 6 of the flywheel 2, respectively.

[Damper Unit 20]

As shown in FIG. 1, the damper unit 20 includes a pair of a clutch plate 21 and a retaining plate 22, a hub flange 23, a plurality of torsion springs 24 and a hysteresis generating mechanism 25.

The friction disc 13, composing part of the torque limiter unit 10, is coupled to the outer peripheral part of the clutch plate 21. The clutch plate 21, having a disc shape, is provided with a plurality of window portions 21 a. The retaining plate 22 is disposed in axial opposition to the clutch plate 21 at an interval. The retaining plate 22, having a disc shape, is provided with a plurality of window portions 22 a. The clutch plate 21 and the retaining plate 22 are fixed to each other by at least one rivet (not shown in the drawings), while being immovable relative to each other in both axial and rotational directions.

The hub flange 23 includes a hub 26 and a flange 28. The hub, having a tubular shape, is provided in the center part of the hub flange 23. The flange 28 extends radially outward from the outer peripheral surface of the hub 26. The hub 26 is provided with a spline hole 26 a on the inner peripheral surface thereof, whereby an input shaft of the drive unit is capable of being spline-coupled to the spline hole 26 a. The flange 28, having a disc shape, is disposed axially between the clutch plate 21 and the retaining plate 22. The flange 28 is provided with a plurality of accommodation portions 28 a. The accommodation portions 28 a are provided in corresponding positions to pairs of the window portions 21 a and 22 a of the clutch plate 21 and the retaining plate 22, respectively.

The plural torsion springs 24 are accommodated in the accommodation portions 28 a of the flange 28, respectively, while being held in both axial and radial directions by the pairs of the window portions 21 a and 22 a of the clutch plate 21 and the retaining plate 22, respectively. Besides, the both circumferential ends of each torsion spring 24 are capable of making contact with circumferential end surfaces of each accommodation portion 28 a and each pair of window portions 21 a and 22 a.

As shown in FIG. 1, the hysteresis generating mechanism 25 includes a first bushing 31, a second bushing 32, a friction plate 33 and a cone spring 34.

The first bushing 31, having an annular shape, is disposed axially between the inner peripheral part of the clutch plate 21 and that of the flange 28 of the hub flange 23. The first bushing 31 is provided with a plurality of engaging protrusions 31 a protruding in the axial direction. Each of the engaging protrusions 31 a is engaged with each of holes provided in the flange 28 through a predetermined gap. Therefore, the first bushing 31 is rotatable relative to the hub flange 23 only in a predetermined angular range.

Both the second bushing 32 and the friction plate 33 are disposed axially between the retaining plate 22 and the flange 28 of the hub flange 23. The second bushing 32, having an annular shape, is provided with a plurality of engaging protrusions 32 a protruding in the axial direction. The engaging protrusions 32 a are engaged with holes provided in the retaining plate 22, respectively. Therefore, the second bushing 32 and the retaining plate 22 are non-rotatable relative to each other. The friction plate 33 is disposed between the flange 28 and the second bushing 32, while being rotatable relative to these members 28 and 32.

The cone spring 34 is disposed axially between the retaining plate 22 and the second bushing 32. The cone spring 34 presses both the second bushing 32 and the friction plate 33 onto the first bushing 31 and presses the first bushing 31 onto the clutch plate 21.

In the hysteresis generating mechanism 25 configured as described above, when the hub flange 23 and both the clutch plate 21 and the retaining plate 22 are rotated relative to each other, friction resistance (hysteresis torque) is generated between the first bushing 31 and the clutch plate 21 and is also generated between the second bushing 32 and the friction plate 33.

[Relation Between Torque Limiter Unit 10 and Knock Pins 6]

Except for the fixation portions 11 b and 15 c of the damper cover 11 and the damper ring 15, the torque limiter unit 10 is disposed in the accommodation portion 5 of the flywheel 2. Now, in assembling the power transmission device 1, the torque limiter unit 10 and the damper unit 20 are firstly assembled as the damper device 3, and then, the damper device 3 is fixed to the flywheel 2. At this time, the knock pins 6 of the flywheel 2 are fitted into pairs of knock pin through holes 11 e and 15 g of the damper cover 11 and the damper ring 15, respectively, whereby the flywheel 2 and the damper device 3 are radially positioned.

Here, the protruding portions 4 d of the bolt fastening portions 4 b of the flywheel 2 protrude radially inward while passing through the first openings 15 d of the damper ring 15, respectively. Because of this, when the flywheel 2 and the damper device 3 has not been radially positioned in assemblage, it is concerned that the protruding portions 4 d of the bolt fastening portions 4 b interfere with the cone spring 14 while protruding radially inward through the first openings 15 d, respectively.

In view of the above, as shown in FIG. 4, length h is set to be shorter than length H, where the length H is defined as the trunk length of each knock pin 6 and the length his defined as the length between the engine-side surface of the cone spring 14 (i.e., the surface facing the interior of the accommodation portion 5) and the engine-side surface of the damper ring 15 (i.e., the surface at which the torque limiter unit 10 is attached to the flywheel 2).

Therefore, when the damper device 3, including the torque limiter unit 10 and the damper unit 20, is accommodated in the accommodation portion 5 of the flywheel 2, the knock pins 6 are firstly fitted into the pairs of knock pin through holes 11 e and 15 g of the damper device 3, respectively. Accordingly, the flywheel 2 and the damper device 3 are radially positioned, and subsequently, the cone spring 14 enters the accommodation portion 5. Therefore, it is possible to avoid interference between the cone spring 14 and the protruding portions 4 d of the bolt fastening portions 4 b of the flywheel 2.

[Actions]

Power, transmitted from the engine to the flywheel 2, is inputted to the damper unit 20 through the torque limiter unit 10. In the damper unit 20, the power is inputted to both the clutch plate 21 and the retaining plate 22, to which the friction disc 13 of the torque limiter unit 10 is fixed, and is then transmitted to the hub flange 23 through the torsion springs 24. Subsequently, the power is further transmitted from the hub flange 23 to the electric motor, the transmission, a power generator and so forth disposed on the output side.

Incidentally, for instance in starting the engine, chances are that an excessive torque is transmitted from the output side to the engine because the amount of inertia is large on the output side. In such a case, the magnitude of torque to be transmitted to the engine side is limited to a predetermined value or less by the torque limiter unit 10.

In the damper unit 20, when the power is transmitted to the torsion springs 24 from the clutch plate 21 and the retaining plate 22, the torsion springs 24 are compressed. Besides, the torsion springs 24 are repeatedly compressed and extended by torque fluctuations. When the torsion springs 24 are compressed and extended, torsion (displacement) is produced between the hub flange 23 and both the clutch plate 21 and the retaining plate 22. The hysteresis generating mechanism 25 is actuated by this torsion and generates a hysteresis torque. Accordingly, torque fluctuations are attenuated.

[Features]

(1) The flywheel 2 reliably has an enough thickness at the bolt fastening portions 4 b. Because of this, even when the damper device 3 is fixed to the flywheel 2 by bolts, this does not result in shortage of strength at the bolt fastening portions 4 b.

On the other hand, the tubular portion 15 b of the damper ring 15, which is the outermost peripheral portion of the body part of the torque limiter unit 10, is provided with the first openings 15 d so as to avoid interference between the damper ring 15 and the bolt fastening portions 4 b (the protruding portions 4 d) of the flywheel 2. This enables increase in outer diameter of the tubular portion 15 b of the damper ring 15. Therefore, a friction disc with a large outer diameter can be employed as the friction disc 13, and compactness in size of the power transmission device can be achieved without impairing the torque capacity.

(2) The damper ring 15 is provided with the second openings 15 e in order to avoid interference between the damper ring 15 and the pawls 12 a of the pressure ring 12. Because of this, it is concerned that the pawls 12 a of the pressure ring 12 are exposed outward and interferes with the inner peripheral surface 4 c of the annular portion 4 of the flywheel 2.

However, the annular portion 4 of the flywheel 2 is herein provided with the recesses 4 e on the inner peripheral surface 4 c, and the recesses 4 e are recessed to the outer peripheral side in positions opposed to the second openings 15 e. Because of this, it is possible to avoid interference of the pawls 12 a of the pressure ring 12 with the annular portion 4 of the flywheel 2.

(3) The damper ring 15 is provided with the first openings 15 d, whereby the protruding portions 4 d of the bolt fastening portions 4 b of the flywheel 2 protrude radially inward while passing through the first openings 15 d of the damper ring 15, respectively. Because of this, it is concerned that in assembling the damper device 3 to the accommodation portion 5 of the flywheel 2, the protruding portions 4 d interfere with the cone spring 14 while protruding radially inward through the first openings 15 d.

However, in assemblage, the knock pins 6 of the flywheel 2 are fitted into the pairs of knock pin through holes 11 e and 15 g of the damper device 3, respectively, before the cone spring 14 is accommodated in the accommodation portion 5 of the flywheel 2, whereby the flywheel 2 and the damper device 3 are radially positioned. Because of this, it is possible to avoid interference between the protruding portions 4 d of the flywheel 2 and the cone spring 14.

Other Preferred Embodiments

The present invention is not limited to the preferred embodiment described above, and a variety of changes or modifications can be made without departing from the scope of the present invention.

(a) In the aforementioned preferred embodiment, the present invention has been applied to the damper device 3 embedded with not only the torque limiter unit 10 but also the damper unit 20. However, the present invention is similarly applicable to a device without embedded with the damper unit 20.

(b) In the aforementioned preferred embodiment, the damper cover 11 and the damper ring 15 are configured to be fixed to the flywheel 2. However, the damper cover 11 and the damper ring 15 can be configured to be fixed to each other in advance, and thereafter, one of the damper cover 11 and the damper ring 15 can be configured to be fixed to the flywheel 2.

REFERENCE SIGNS LIST

-   1 Power transmission device -   2 Flywheel -   3 Torque limiter embedded damper device -   4 Annular portion -   4 b Bolt fastening portion (attachment portion) -   4 c Annular portion inner peripheral surface -   4 d Protruding portion -   5 Accommodation portion -   6 Knock pin -   6 a Trunk portion -   10 Torque limiter unit -   11 Damper cover (first plate) -   12 Pressure ring (second plate) -   13 Friction disc -   14 Cone spring (pressing member) -   15 Damper ring (third plate) -   15 a Support portion -   15 b Tubular portion -   15 c Fixation portion p0 15 d First opening -   15 g Knock pin through hole 

What is claimed is:
 1. A torque limiter fixed to a flywheel including an annular portion to which a plurality of knock pins each including a trunk portion are fixed and an accommodation portion provided on an inner peripheral side of the annular portion, the torque limiter disposed in an interior of the accommodation portion except for a part thereof fixed to the flywheel, the torque limiter comprising: a first plate to which a torque is inputted from the flywheel; a second plate axially opposed to the first plate; a friction disc disposed between the first plate and the second plate; a pressing member configured to press the second plate onto the friction disc; and a third plate configured to interpose and hold the pressing member together with the second plate therebetween, the third plate provided with a plurality of knock pin through holes in an outer peripheral part thereof such that the plurality of knock pins are fitted therein at the trunk portions thereof, the outer peripheral part attached at an attachment surface thereof to the annular portion of the flywheel, wherein a length between a surface of the pressing member and the attachment surface of the third plate is shorter than a length of the trunk portion of each of the plurality of knock pins, the surface of the pressing member facing the interior of the accommodation portion.
 2. The torque limiter according to claim 1, wherein the annular portion of the flywheel includes a plurality of attachment portions circumferentially aligned, each of the plurality of attachment portions including a protruding portion protruding radially inward, the third plate includes a support portion configured to support the pressing member, a tubular portion provided in an outer peripheral part of the support portion, the tubular portion covering an outer peripheral surface of the friction disc, the tubular portion axially extending and opposed to an inner peripheral surface of the annular portion of the flywheel, and a fixation portion provided with the plurality of knock pin through holes, the fixation portion fixed to the flywheel, and the tubular portion includes a plurality of openings circumferentially aligned, each of the plurality of openings disposed in a corresponding position to the protruding portion so as to avoid interference between the third plate and the protruding portion.
 3. The torque limiter according to claim 2, wherein an outer peripheral surface of the tubular portion of the third plate has a diameter greater than a minimum inner diameter of the protruding portion.
 4. The torque limiter according to claim 2, wherein the pressing member is a cone spring disposed in an interior of the tubular portion of the third plate.
 5. The torque limiter according to claim 2, wherein the first plate is fixed together with the fixation portion of the third plate to the flywheel.
 6. The torque limiter according to claim 1, wherein the first plate and the second plate are non-rotatable relative to each other.
 7. A torque limiter embedded damper device comprising: the torque limiter recited in claim 1; and a damper unit configured to attenuate fluctuations in rotation transmitted thereto, the damper unit provided on an output side of the torque limiter.
 8. A power transmission device comprising: a flywheel including an annular portion to which a plurality of knock pins each including a trunk portion are fixed and an accommodation portion provided on an inner peripheral side of the annular portion; and the torque limiter recited in claim 1, the torque limiter configured to transmit the torque inputted thereto from the flywheel to an output-side member. 